Enhanced X and Ku band microwave absorption powered by a magnetic–dielectric synergistic effect in Pr-doped M/W composite hexaferrites

Abstract

Using single loss type media as microwave absorbers to simultaneously achieve low reflection loss, wide-band absorption and thin thickness is a huge challenge. In this work, to combine the high dielectric loss of Pr-doped M-type strontium ferrite and the high magnetic loss of W-type hexaferrites, we improved the traditional sol–gel auto-combustion method via increasing an extra sintering process and successfully prepared xSrPr_0.5Fe_11.5O₁₉/yBaCo₂Pr_0.5Fe_15.5O₂₇ (x : y = 2 : 1, 1.5 : 1, 1 : 1, 1 : 1.5 and 1 : 2) M/W (M-type hexaferrite/W-type hexaferrite) composite materials with a unique “inlay structure”. The M-phase and PrFeO₃-type phase were partially wrapped by the huge W-phase, which resulted in enhanced exchange coupling. Benefitting from the exchange coupling and huge grains, the coercivity and anisotropy fields of composite hexaferrites decreased. Therefore, the natural resonance frequencies of some samples reduced to within 18.00 GHz. High magnetic loss occurs while dielectric loss is preserved due to strong resonance interaction and multiple polarization relaxation mechanisms. Hence, the composite hexaferrites exhibit satisfactory microwave absorption performance on account of the magnetic–dielectric synergistic effect. The effective absorption bandwidth of the prepared materials can cover X and Ku bands at thin matching thicknesses (<2.00 mm). The minimum reflection loss reaches −56.30 dB (d = 1.97 mm), and the maximum effective absorption bandwidth reaches 8.17 GHz (d = 1.63 mm). This work will provide new ideas for improving the absorption performance of ferrite composite materials.